It was then that he slipped his legs off the side of the bay window, rising and standing like a tower before his curious little sister.
The two were caught in the eye of a clothing storm, his shirts strewn about the floor around their feet. There wasn't much to note about the bedroom aside from maybe the solar system model pitched over his window and the lonely light bulb fished from the ceiling to spread light over his odds and ends.
The blonde girl started, “Do you wanna play--?”
“Not really.”
Maybe it could use another edit, but is this on the right track?
As for yours, I think it has a very enticing start, and it definitely kept my eyes going all the way through! Only real roadbumps I encountered:
Might be a personal thing, but the line reading, "Somewhere close by a horse screeched in terror" rubbed me strangely. I think it's because "somewhere close by" is a formal phrasing and detracts from the danger.
Did you mean "feint waver" or "faint waver"?
"Raining randomly" is good alliteration, but I'd avoid the word "randomly" in an apocalyptic scene because it has a casual connotation to me. There might be a better trade-off there, I'm not sure.
Might be another personal preference, but "One of the balls of fire was sailing down right towards them with no hope of evasion" could instead be something like, "It came sailing down upon them - their deaths soon to arrive in the form of a ball of molten destruction."
Otherwise, tremendous job. The terror of the apocalyptic scenario reminds me of Attack on Titan, and I'm a big fan of that kind of world-building (or world-destroying!)
